Evaluation of retinal image degradation by higher-order aberrations and light scatter in chick eyes after photorefractive keratectomy (PRK)

摘要

Intraocular light scatter can severely degrade retinal image quality, a key determinant of visual performance and eye growth regulation, yet it is often ignored in analyses of retinal image quality. A method for characterizing ocular light scatter using Shack-Hartmann images is described here. A local light scatter map is derived by de-convolving the dots in the Shack-Hartmann image recorded from a real eye with those from a model eye, and used to estimate overall ocular light scatter. As an index of retinal image quality, the modulation transfer function (MTF) of the eye is derived as the product of MTFs for light scatter and aberrations alone and for comparative purposes, an MTF volume ratio, equivalent to the Strehl ratio computed in the frequency domain, is computed. These analyses were applied to Shack-Hartmann images collected from three chick eyes, one day before and four days after photorefractive keratectomy (PRK) surgery. PRK was performed on one eye of each of three 4-week-old chicks; ablation parameters for a clinical argon fluorine excimer laser system from Visx were adjusted based on the results of ablations performed on enucleated chick eyes of the same age. While all three eyes showed increased higher order aberrations after PRK, only two eyes showed significantly increased light scatter. The proposed method for characterizing retinal image quality was able to capture these interocular differences.